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Instrumental Analysis > Molecular Fluorescence and Phosphorescence (5) > Flashcards

Molecular Fluorescence and Phosphorescence (5) Flashcards

1
Q

What is photoluminescence?

A

process where molecules are elevated to excited state; excess energy emitted as radiation of wavelength different than wavelength of absorption; excitation/de-excitation process involving photons

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2
Q

de-excitation process that occurs after excitation by photons

A

photoluminescence

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3
Q

de-excitation process that occurs after excitation by high energy particles

A

radioluminescence

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4
Q

de-excitation process that occurs after excitation by chemical process

A

chemiluminescence

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5
Q

what is the total spin quantum number S?

A

sum of net spin

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6
Q

What is S for uncharged molecules?

A

0

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7
Q

How is multiplicity calculated?

A

2S + 1 = x where x is like singlet, triplet, etc

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8
Q

What is a singlet state?

A

multiplicity of one

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9
Q

What is S0?

A

ground

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10
Q

What is S1?

A

excited state 1

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11
Q

What is S2?

A

excited state 2

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12
Q

What is a triples tate?

A

formed when an excited electron reverses its spin

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13
Q

what is the quantum mechanical selection rule for single and triplet states?

A

ΔS=0

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14
Q

What is the time scale for electronic absorption?

A

10^-15 seconds

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15
Q

What is a Jablonski diagram?

A

qualitative depiction of absorption and emission processes

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16
Q

What is vibrational relaxation?

A

molecule rapidly and nonradiactively dissipates excess vibrational energy as heat by collision with solvent molecules

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17
Q

What is the time scale for vibrational relaxation?

A

10^-12 seconds

18
Q

What is internal conversion?

A

molecule intermolecularly passes from original excited state to a lower one of the same multiplicity

19
Q

What is the time scale for internal conversion?

A

10^-12 seconds

20
Q

What is fluorescence

A

process of photon emission for de-excitation S1 to S0

21
Q

How does the wavelength of fluorescence emission compare with wavelength of initial absorption and why?

A

at lower energy and longer wavelength because of vibrational relaxation

22
Q

What is the 0-0 transition?

A

fluorescence and absorption between two electron states that have at least one transition of the same energies; between v” = 0 S0 and v’ = 0 S1

23
Q

What is the time scale for fluorescence?

A

10^-9 seconds

24
Q

What is external conversion?

A

energy transfer between excited molecules and solvents

25
Q

How does external conversion differ from internal conversion?

A

external is de-excitation between excited molecule and other solvents, internal is lowering from original excited to a lower excited state of the same multiplicity (S2 to S1)

26
Q

What is intersystem crossing?

A

molecule in excited state may change spin multiplicity from single to triplet

27
Q

What is the time scale for intersystem crossing?

A

varies but can be 10^-10 seconds with heavy or paramagnetic molecules

28
Q

What is phosphorescence?

A

From triplet, molecule rapidly relaxes to lowest vibrational level

29
Q

From which spin state does phosphorescence occur?

A

T1 to S0

30
Q

What is the time scale of phosphorescence?

A

10^-3 to 10 seconds

31
Q

Why is phosphorescence frequently carried out at liquid nitrogen temperatures?

A

cannot be seen in fluid solutions at room temperature because there are many deactivation processes that have faster rate constants

32
Q

What is quenching?

A

non radiative process that depopulates S1 or T1 levels and competes with fluorescence and phosphorescence

33
Q

What governs the observed intensities in electronic processes?

A

overlap of vibrational wave functions in upper and lower states according to frank-condos principle (about geometry changes)

34
Q

What is the stokes loss/shift?

A

difference in energy between position of maximum emission and 0-0 transition

35
Q

what does stokes shift measure?

A

change in geometry of equilibrium configurations of ground and excited states

36
Q

What kinetic rate law describes fluorescence?

A

pseudo first order kinetics

37
Q

What is the fluorescent quantum yield?

A

fraction of total number of photons absorbed that result in fluorescent emission

38
Q

How is fluorescent quantum yield defined?

A

total number of fluorescent photons emitted / total number photons absorbed

39
Q

How is the steady state fluorescent lifetime related to the kinetic rate constants of the de-excitation process?

A

inverse

40
Q

How is the fluorescent quantum yield related to the steady state lifetime?

A

quantum yield = steady state lifetime divided by radiative lifetime

Instrumental Analysis (45 decks)

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